Researchers at the University of Illinois at Urbana-Champaign have used a new printing process to assemble tiny solar cells into multilayered stacks with extraordinary levels of photovoltaic conversion efficiency.

The solar cells use multiple junctions to harvest a broader spectrum of sunlight, allowing them to reach power conversion efficiencies of around 44% compared to the 29% of conventional silicon and thin-film single-junction solar cells.

Although not yet validated by external labs, the researchers claim the results are the best ever recorded for any kind of photovoltaic technology.

University Professor John Rogers worked in collaboration with Semprius and Solar Junction to develop the micro transfer printing technique, which is used to manipulate and layer ultrathin semiconductor elements on top of one another in a lattice-like composition.

The high-speed process bonds together thousands of compound semiconductor materials to produce a three-junction microcell that is then stacked on top of a single junction microcell made from germanium.

An infrared transparent and refractive-index-matched layer of a chalcogenide glass serves as a thermally conductive and electrically insulating interface layer within the stacks.

To work, the junctions must be matched exactly to their neighbour, something which grows in difficulty as the number of junctions increases.

Despite the challenge, the research team is continuing to work towards producing devices with five or six such solar cell junctions, to further improve efficiency.